The present invention relates to an insulated container used for example as a cooler box, a thermos bottle or an insulated lunch box, a suitable insulating material for such a container and a method for its manufacture. More particularly the present invention relates to an insulated container wherein an insulating material, made by filling a gas having a lower thermal conductivity than that of air into a bag having gas barrier properties, is disposed between inner and outer walls of a double walled container having inner the outer walls joined together as one. The invention also relates to the insulating material used in the container and the method of manufacturing the container.
Heretofore, there have been available insulated containers such as cooler boxes made with inner and outer walls of a synthetic resin, with the space between the inner and outer walls filled with, an organic foam material such as rigid urethane foam or polystyrene foam, or an inorganic powder such as perlite, to thereby form an insulating layer.
Moreover there are also available insulated containers wherein the inner and outer wall are made from a metal material, with the space between forming a vacuum insulating layer.
However, with the former insulated container which is filled with an insulating material such as foam, since the thermal conductivity of the insulating material is high, then a thick insulating layer is required to increase the insulating performance of the container. Moreover, when filling the foam material and the like into the space between the inner and outer walls, the insulating layer must be of a predetermined thickness to enable an efficient filling operation. As a result, the insulating layer must be made from 5 to 10 times thicker than that for an insulated container having a vacuum insulating layer. Therefore, in the case of insulated containers filled with an insulating material, the volumetric efficiency, namely, the ratio of the inside container volume to the total volume with the opening closed, is reduced, so that such containers are generally not suitable for portable use.
With the latter insulated container having a vacuum insulating layer, excellent insulating performance is possible even if the insulating layer is made thin, so that the container is ideal for portable use. However there are problems due to difficulties with manufacture and high cost. Furthermore, since the inner and outer walls are subjected to atmospheric pressure loadings, the shape of the inner and outer walls is restricted to a pressure resistant structure which can resist the atmospheric pressure loadings. It is therefore difficult to make a convenient rectangular box like shape container with plain walls.